As for the buffer layer of a CIS-based thin-film solar cell device, and a manufacturing method thereof, there are known Patent Documents 1, 2 and 3 proposed by the present applicant. For example, in Patent Document 1, it is disclosed that the buffer layer of the CIS-based thin-film solar cell device is formed of a zinc mixed crystal compound semiconductor thin film, and that a part of hydroxides in the zinc mixed crystal compound semiconductor thin film have been reformed into oxides. As the method for depositing the zinc mixed crystal compound semiconductor thin film, there is disclosed the following method: a zinc salt and a sulfur-containing salt are mixed with an appropriate complex forming agent, so that a zinc ammonia complex salt is formed in a solution containing a zinc salt and a sulfur-containing salt dissolved therein; a first multinary compound semiconductor thin film to serve as a light absorbing layer is brought in contact therewith in the solution, so that a zinc mixed crystal compound semiconductor thin film containing oxygen, sulfur, and a hydroxy group is grown from the solution on the first multinary compound semiconductor thin film; then, the first multinary compound semiconductor thin film on which the zinc mixed crystal compound semiconductor thin film has been grown is annealed in air, thereby to reform a part of hydroxides in the zinc mixed crystal compound into oxides; and resultantly, a high-resistance zinc mixed crystal compound containing oxygen, sulfur, and hydroxyl group is produced.
Whereas, Patent Document 2 discloses as follows: on a first multinary compound semiconductor thin film to serve as a light absorbing layer, a zinc mixed crystal compound semiconductor thin film to serve as a buffer layer (interface layer) is chemically grown from a strongly alkaline solution mixture; the strongly alkaline solution mixture is a solution obtained by mixing a solution of a zinc salt dissolved in an aqueous ammonia or an ammonium hydroxide solution with an aqueous solution of a sulfur-containing salt dissolved in pure water; and the zinc mixed crystal compound semiconductor thin film is deposited with the transparency of the solution mixture being within the range of 100% to 50%.
Further, Patent Document 3 discloses as follows: on a first multinary compound semiconductor thin film to serve as a light absorbing layer, the sulfur-containing zinc mixed crystal compound semiconductor thin film is chemically grown from a solution; then, the sulfur-containing zinc mixed crystal compound semiconductor thin film is annealed in vacuum of 1 to 100 Torr at a temperature of 100 to less than 250° C. for 10 to 120 minutes, thereby to convert zinc hydroxide in the sulfur-containing zinc mixed crystal compound semiconductor thin film into zinc oxide; and resultantly, a buffer layer (interface layer) which is transparent and has high resistance is formed.
Patent Document 1: Japanese Patent No. 3249342 (JP-A-8-330614)
Patent Document 2: Japanese Patent No. 3311286 (JP-A-11-145493)
Patent Document 3: JP-A-2002-343987
In such a buffer layer or a CIS-based thin-film solar cell device manufactured by a deposition method of the buffer layer, generally, in the deposition step of a CIS-based light absorbing layer, deposits of simple substances such as sulfur and selenium, compounds thereof, and the like are deposited on the surface of the CIS-based light absorbing layer. Further, colloidal solid matter is also deposited on the surface of the buffer layer during the buffer layer deposition. In this respect, when it is possible to remove the deposits at the junction of the CIS-based light absorbing layer and the buffer layer, and to remove the deposits on the buffer layer surface, conceivably, the high resistance at the buffer layer-covered part can be held, and the conversion efficiency of the CIS-based thin-film solar cell device can be improved. However, such a technology has not yet been disclosed.